1. Field of the Invention
This invention relates to a copying machine employing an electrophotographic process, and more particularly to a copying apparatus adopting an electrophotographic process using a sensitive screen having a plurality of apertures.
2. Description of the Prior Art
Known as the typical conventional electrophotography are a direct process such as for example electrofax and an indirect process such as xerography. The former direct process uses a specifically treated recording material coated with a photoconductive material such as zinc oxide. This process, therefore, has a problem in the image contrast as the image formed on the recording material lacks brightness. Moreover, due to the specific treatment, the recording material is heavier than the conventional paper and different in feed from the usual paper. Acccording to the latter indirect process, a high contrast and high quality image is obtained as it uses a usual paper as the recording material to form an image. However, in this indirect process, when a toner image is transferred to the recording material, the recording material contacts with the surface of the photosensitive member and further, cleaning means strongly contacts with the surface of the photosensitive member when the remaining toner is cleaned off, so that the photosensitive member is subject to damage each time the transfer and cleaning is practiced. Therefore, the duration of an expensive photosensitive member becomes shortened, resulting in high cost for forming an image.
The improvements for removing said drawbacks of the conventional processes were proposed in U.S. Pat. Nos. 3,220,324, 3,680,954 and 3,645,614. In these patents, a photosensitive member of a screen type or a grid type having a number of fine meshed openings is used. The electrostatic latent image is formed on a recording material by modifying ion flow through the screen or grid, and thereafter the recording material formed with the latent image is visualized. There is no necessity to develop and clean the screen or grid which corresponds to the photosensitive member, so that the duration of the screen or grid is prolonged.
In U.S. Pat. No. 3,220,324, a conductive screen coated with a photoconductive material is used, and an image exposure simultaneously with corona ion from the corona discharger is applied to a recording material through said screen. The corona ion flow is modified by the screen and an electrostatic latent image is formed on the recording member.
According to U.S. Pat. No. 3,680,954, a conductive grid coated with a photoconductive material and a conductive controlling grid are used, an electrostatic latent image is formed on the grid in the image form, and the different electric fields are formed on the grid and the controlling grid so as to modify the corona ion flow to form an image on a recording member.
In U.S. Pat. No. 3,645,614, the screen comprises an insulating material overlaid with a conductive material and the insulating material comprises a photoconductive material. An electric field preventing the passing of ion flow is formed at the openings for passing the ion flow as the electrostatic latent image is formed on the screen.